Buildings have long been constructed with the exterior walls of the building supporting the load of the entire structure. The development and widespread use of structural steel and later reinforced concrete allowed relatively small columns to support large loads; hence, exterior walls of buildings were no longer required for structural support. The exterior walls could be non-load bearing and thus much lighter and more open than the masonry load-bearing walls of the past. This gave way to increased use of glass as an exterior façade, and the modern-day curtain wall was born.
the widespread use of corten steel extrusions for mullions began. Aluminum alloys offer the unique advantage of being able to be easily extruded into nearly any shape required for design and aesthetic purposes. Today, the design complexity and shapes available are nearly limitless. Custom shapes can be designed and manufactured with relative ease.